PDF export: PDF and .ai files keep the document's creation date

The engine built the PDF options without a creation date, so the
writer dated every PDF and PDF-compatible .ai file with the time it
was written. A document created on 2020-01-01 (File › File Info
shows the date) exported as a PDF with today's date in /CreationDate
and xmp:CreateDate. SVG export with the metadata option already
writes the document's own date.

The options now carry the document's File Info created date and the
time of writing as the modification date. A document without a
creation date is dated with the time of writing, as before, so PDF/X
files still get their required date. The PDF writer writes one date
for both, so the export then sets /ModDate, xmp:ModifyDate and the
PDF/A history dates to the time of writing; /CreationDate and
xmp:CreateDate keep the document's date. The page information mark
and the embedded editing data's modification date keep the time of
writing.

Docs: docs/mcp.md (File Info), docs/target-app-parity.md.

docs/mcp.md

@@ -2599,7 +2599,9 @@ ISO 8601 UTC. Pass any of the editable keys to change them in one undo step (`nu
 list or a comma-separated string and keeps each word once); bad values are refused. PDF export writes the title,
 author, description and keywords to the document info and XMP, PNG export writes them (with the copyright and
 creation date) as text chunks, and SVG export writes the description as `<desc>` and, with the `metadata` option,
-all of it as Dublin Core. A PDF, `.ai` or `.ait` opened from its pages or its editing copy (`document.open`,
+all of it as Dublin Core. PDF export and PDF-compatible `.ai` and `.ait` saves write the `created` date (the time of
+writing when the document has none) as the file's creation date and the time of writing as its modification date.
+A PDF, `.ai` or `.ait` opened from its pages or its editing copy (`document.open`,
 `file.newFromTemplate`, `file.revert`; not one restored from the document it carries) opens with the `author`,
 `description`, `keywords`, `copyrightStatus`, `copyrightNotice`, `copyrightUrl`, `created` and `modified` that its XMP
 packet (`dc:creator`, `dc:description`, `dc:subject` or `pdf:Keywords`, `xmpRights:Marked`, `dc:rights`,

docs/target-app-parity.md

@@ -722,6 +722,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - File › Place with Bounding Box (`file.place {crop: "bounding"}`) measures the art that shows, with its strokes and effects, as an export does: hidden objects, guides and template layers do not count, a group whose only part on the page or artboard is hidden is not placed, and symbol instances are measured by their art, for `at`, `rect`, the place cursor and `file.place.info` (`crates/engine/src/tests_place.rs`).
   - Desktop print transport uses `craft-print` for CUPS and modern Windows. Sheet composition, copies, separations and colour management remain in VectorCraft; Windows 7 retains WMI and the installed PDF viewer. The print-preview and physical-device fidelity gaps remain, so print scores and hours are unchanged.
   - A PDF, PDF-compatible `.ai` or `.ait` opened from its pages or its editing copy opens with the File Info that its XMP packet and its document information dictionary give: the author, description, keywords, copyright status, notice and URL, and the created and modified dates, the XMP packet's value where both give one; the title is not changed (`crates/pdf/src/tests_file_info.rs`, `crates/engine/src/tests_fileinfo.rs`).
+  - PDF export and PDF-compatible `.ai` and `.ait` saves write the document's File Info created date as the file's creation date, or the time of writing when the document has none, and the time of writing as its modification date; the page information mark still prints the time of writing (`crates/engine/src/tests_fileinfo.rs`, `crates/pdf/src/tests.rs`, `crates/pdf/src/tests_marks.rs`).
   - Opening a PDF or PDF-compatible `.ai` whose XMP packet nests elements more than 256 deep no longer overflows the stack: File Info leaves the packet out and takes the document information dictionary's values (`crates/pdf/src/tests_file_info.rs`).
   - `file.print`, `print.preview` and `print.setup` take a print preset by name (`preset`: `[Default]` or a saved preset, in any case): its settings are used instead of the document's, with `settings` over them, `print.setup` saves them with the document, and an unknown name is refused with the list of presets.
   - Place and the Links panel, Package (placed `.vectorcraft` documents packaged with their own linked files and fonts, relinked to the copies: #777), File Info, Print with print presets, PostScript output and print tiling, slices and Save for Web, Export for Screens and Asset Export, CSS Properties, PNG/PDF/SVG/text clipboard flavours; files copied in a file manager paste as art (SVG, PDF, EMF/WMF, bitmaps) on every desktop platform, and Linux/Wayland reads the compositor's clipboard (#398); on Linux the Paste menu checks the clipboard off the UI thread, so an X11 owner that never answers can't freeze the window (#510); screenshots and other copied pictures paste as embedded images at the view centre everywhere, the web included (#457).